Traceless Vulcanization Strategy for Disulfide Cross-Linked Polyisobutylene Biomedical Elastomers

A self-cross-linking polyisobutylene thiol (PIB thiol) was developed in this work from brominated isobutylene-co-para methylstyrene (BIMSM rubber). Nucleophilic substitution of BIMSM benzylic bromides using sulfur-based nucleophiles yields a shelf-stable intermediate PIB xanthate, which can be readily cleaved to produce thiol-grafted PIB. The PIB thiols oxidatively dimerize at elevated temperatures to yield a cross-linked network, reinforced solely through disulfide linkages. In the absence of accelerators, elemental sulfur, and other additives, this “traceless vulcanization” affords networks with up to 99% gel fractions and mechanical properties that can reach up to 1000 kPa in tensile strength, 1200% elongation, and shape recovery. Rheological analysis and cross-link density characterization provided insights into the reinforcement nature of a purely disulfide network in butyl rubbers with high creep resistance, along with low tan(δ) values across a wide range of temperatures and test frequencies.